Milling Tool

ABSTRACT

A milling tool for enlarging portions of a wellbore. The milling tool includes a housing that defines a central bore along its length. A piston is moveably disposed within the central bore, and axial movement of the piston moves support arms radially outwardly from the housing. The support arms carry milling blades for enlarging portions of a wellbore.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the design of milling tools used forenlarging subterranean wellbores.

2. Description of the Related Art

Milling tools are used to enlarge or reopen sections of subterraneanwellbores. In some instances, milling tools are used to remove casingfrom sections of wellbores.

SUMMARY OF THE INVENTION

The invention provides improved milling tools and methods for operationof these tools. An exemplary milling tool is described which has supportarms that are moveable radially outwardly from a housing. The supportarms have milling blades that carry milling cutters that can cut awaythe surrounding wellbore. In a described embodiment, there are threemilling blades mounted on each of the support arms. Also in a describedembodiment, each of the milling blades has a length that is at leastone-fifth of the length of the housing. In a particular embodiment, themilling blades are at least a foot in length. Additionally, the millingblades are preferably affixed to the support arms using a dovetailconnection.

The milling arms are moved radially outwardly by a translation mechanismthat uses fluid pressure to mechanically urge the milling arms radiallyoutwardly from the housing. In a described embodiment, the translationmechanism includes a piston that is axially moveable with respect to thehousing. A piston chamber is defined within the housing of the millingtool, and an enlarged diameter piston portion is located within thepiston chamber. In a described embodiment, the piston is shifted withrespect to the housing by injection of pressurized fluid through thepiston and into the piston chamber. Fluid pressure is applied to theenlarged diameter piston portion and shifts the piston axiallydownwardly with respect to the housing. Downward movement of the pistoncauses the support arms to be urged radially outwardly. Rotation of themilling tool with the support arms radially extended will enlarge thesurrounding borehole.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and further aspects of the invention will be readilyappreciated by those of ordinary skill in the art as the same becomesbetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings in whichlike reference characters designate like or similar elements throughoutthe several figures of the drawing and wherein:

FIG. 1 is a side, cross-sectional view of a subterranean wellborecontaining a running string with an exemplary milling tool constructedin accordance with the present invention.

FIG. 2 is a side, cross-sectional view of an exemplary mill constructedin accordance with the present invention with the mill being in anundeployed condition.

FIG. 3 is a side, cross-sectional view of the mill shown in FIG. 2, nowin a deployed condition.

FIG. 4 is an axial cross-section taken along lines 4-4 in FIG. 2.

FIG. 5 is an axial cross-section taken along lines 5-5 in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an exemplary wellbore 10 that has been drilledthrough the earth 12. A running string 14 is shown disposed within thewellbore 10. The running string 14 in FIG. 1 is constructed of coiledtubing. However, it will be understood by those of skill in the art thatthe running string 14 might also be constructed of standard productiontubing string sections. A fluid flowbore 16 is defined along the lengthof the running string 14. The running string 14 includes a milling tool18 that is constructed in accordance with the present invention. Themilling tool 18 is used to enlarge sections of the wellbore 10.

An exemplary milling tool 18, constructed in accordance with the presentinvention is shown in greater detail in FIGS. 2-5. The milling tool 18includes a tubular housing 20 that defines an axial central bore 22along its length. In the depicted embodiment, the housing 20 is includesan upper end cap 24 that is threadedly secured to a blade housing 26.The lower end of the blade housing 26 is threadedly affixed to a lowerpiston housing 28.

A piston 30 is disposed within the central bore 22 and is axiallymoveable between an upper position shown in FIG. 2, and a lower positionshown in FIG. 3. The piston 30 includes an upper flow tube portion 32,an enlarged diameter piston portion 34 and a lower flow tube portion 36.An axial flow passage 38 is defined along the length of the piston 30.Lateral flow openings 40, 42 are formed in the upper flow tube portion32 and permit fluid communication between the flow passage 38 and theradial exterior of the piston 30. The upper flow tube portion 32presents an outwardly projecting flange 44. A fluid flow restriction 45is provided within the flow passage 38.

An enlarged diameter piston chamber 46 is formed within the lower pistonhousing 28, and the piston portion 34 is disposed within the pistonchamber 46. The piston portion 34 seals against the sidewall of thepiston chamber 46. A compressible spring 48 also resides within thepiston chamber 46 and biases the piston portion 34 of the piston 30axially upwardly within the piston chamber 46 so that the piston 30 isbiased toward the upper position shown in FIG. 2.

A plurality of windows 50 are formed in the blade housing 26. In thedepicted embodiment, there are three windows 50. However, those of skillin the art will understand that there may be more or fewer than three. Asupport arm 52 is located within each of the windows 50. Each supportarm 52 is radially moveable within its window 50 between a radiallyretracted position (FIG. 2) and a radially extended position (FIG. 3).

Milling blades 54 extend radially outwardly from each of the supportarms 52. In the depicted embodiment, there are three milling blades 54that are secured to each support arm 52, resulting in nine total millingblades 54. In a current embodiment, a dovetail attachment is used tosecure the milling blades 54 to their support arms 52. Hardened millingcutters 56, of a type known in the art, are secured to each of themilling blades 54. In a particular embodiment, the milling blades 54have a length that is approximately one-fifth of the total length of thehousing 20 or greater. Also in a particular embodiment, the millingblades 54 are at least one foot in length.

A wedge member 58 is located axially adjacent each of the cutting arms52. The wedge member 58 presents an angled, downwardly-facing slotsurface 60 into which the cutting arm 52 is disposed. The upper end ofthe wedge members 58 are in contact with the flange 44 of the piston 30.The lower end of each blade window 50 presents an angled upwardly-facingsurface 62. When the piston 30 is moved axially downwardly within thehousing 20, the flange 44 urges the wedge members 58 axially downwardlyas well, and the support arms 52 are urged radially outwardly in eachblade window 50 due to sliding action along each of the angled surfaces60, 62.

In operation, the running string 14 and attached milling tool 18 arelowered into the wellbore 10 until the milling tool 18 is locatedadjacent a portion of the wellbore 10 which it is desired to enlarge.Pressurized fluid is flowed into the flowbore 16 of the running string14. Fluid passes downwardly through the axial flow passage 38 of thepiston 30 and outwardly through lower lateral flow opening 42 into thepiston chamber 46. Fluid pressure will build up above the flowrestriction 45. In addition, fluid pressure will be exerted upon theenlarged diameter piston portion 34 to also urge the piston 30 axiallydownwardly to compress the spring 48 (see FIG. 3). Applying pressure tothe enlarged piston portion 34 to activate the milling tool 10 permitssignificant force to be generated to move the support arms outwardly.Downward movement of the piston 30 with respect to the housing 20 willmove the support arms 52 radially outwardly so that the cutters 56 ofmilling blades 54 are placed into cutting engagement with the wellbore10. Rotation of the running string 14 will cause the cutters 56 to cutaway and enlarge portions of the wellbore 10.

When milling is complete, the support arms 52 can be retracted byreducing fluid pressure within the flowbore 16 of the running string 14.The spring 48 will urge the piston 30 axially upwardly and back to theinitial position shown in FIG. 2, thereby permitting the support arms 52to move radially inwardly.

In addition to the milling tool 18, the invention provides a millingassembly that is useful for enlarging sections of a wellbore 10. In adescribed embodiment, a milling assembly is made up of a running string14 and a milling tool 18 that is affixed to the running string 14.

The foregoing description is directed to particular embodiments of thepresent invention for the purpose of illustration and explanation. Itwill be apparent, however, to those skilled in the art that manymodifications and changes to the embodiment set forth above are possiblewithout departing from the scope and the spirit of the invention.

What is claimed is:
 1. A milling tool comprising: a housing defining acentral bore along its length; a piston moveably disposed within thebore between a first position and a second position; a support arm thatis moveable radially outwardly from the housing when the piston is movedto the second position; and a milling blade affixed to the support armand having at least one milling cutter for milling a surrounding portionof wellbore.
 2. The milling tool of claim 1 wherein there are threemilling blades affixed to the support arm.
 3. The milling tool of claim1 further comprising: a piston chamber formed within the bore; and thepiston having an enlarged diameter piston portion that resides withinthe piston chamber.
 4. The milling tool of claim 3 wherein the piston ismoved from the first position to the second position by fluid pressureupon the enlarged diameter piston portion.
 5. The milling tool of claim4 wherein fluid is flowed through an axial flow passage formed withinthe piston to enter the piston chamber.
 6. The milling tool of claim 1wherein the milling blade has a length that is at least one-fifth of thelength of the housing.
 7. The milling tool of claim 1 wherein there arethree support arms.
 8. The milling tool of claim 3 further comprising acompressible spring that biases the enlarged diameter piston portionaxially such that the piston is biased toward the first position.
 9. Amilling assembly for enlarging a portion of a wellbore, the millingassembly comprising: a running string having a central flowbore definedalong its length; a milling tool affixed to the running string, themilling tool comprising: a housing defining a central bore along itslength; a piston moveably disposed within the bore between a firstposition and a second position; a support arm that is moveable radiallyoutwardly from the housing when the piston is moved to the secondposition; and a milling blade affixed to the support arm and having atleast one milling cutter for milling a surrounding portion of wellbore.10. The milling assembly of claim 9 wherein there are three millingblades affixed to the support arm.
 11. The milling assembly of claim 9further comprising: a piston chamber formed within the bore; and thepiston having an enlarged diameter piston portion that resides withinthe piston chamber.
 12. The milling assembly of claim 11 wherein thepiston is moved from the first position to the second position by fluidpressure upon the enlarged diameter piston portion.
 13. The millingassembly of claim 12 wherein fluid is flowed through an axial flowpassage formed within the piston to enter the piston chamber.
 14. Themilling assembly of claim 9 wherein the milling blade has a length thatis at least one-fifth of the length of the housing.
 15. The millingassembly of claim 9 wherein there are three support arms.
 16. Themilling assembly of claim 11 further comprising a compressible springthat biases the enlarged diameter piston portion axially such that thepiston is biased toward the first position.